1. Field of the Invention
The present invention relates generally to a process of making a ferroelectric electronic component and the product of that process and, more particularly, to an improved process characterized by the separate formation of two subassemblies and then connecting these to form the final products by placing one subassembly on top of the other.
2. The Prior Art
In the late 1960's, a new ceramic ferroelectric composition in the form of a thin film had been developed for use in logic and memory devices. See D. W. Chapman, "Some Thin-Film Properties of a New Ferroelectric Composition," J. Appl. Phys., Vol. 40, No. 6 (May 1969), pp. 2381-2385. Ferroelectric materials are crystalline substances displaying ferroelectricity, i.e., spontaneous electric polarization.
During the next two decades, workers in the field experimented with ferroelectric materials for thin film devices including barium titanate for thermistors, lead titanate for pyroelectric detectors, bismuth titanate for nonvolatile memory devices and lead zirconate titanate (PZT) for capacitors, electro-optic and nonvolatile memory devices. See S. B. Krupanidhi et al, "rf planar magnetron sputtering and characterization of ferroelectric Pb (Zr, Ti) O.sub.3 films, "J. Appl' Phys' 54 (11), November 1983, pp. 6601-6609. Fabrication of such ferroelectric thin film devices included vacuum deposition techniques such as electron beam evaporation, ion-beam deposition, rf sputtering and chemical vapor deposition, and also chemical sol gel processing and coating. See, inter alia, U.S. Pat. Nos. 3,368,920 that issued to A. K. Hagenlocher in Feb. 13, 1968; 3,997,690 that issued to Chen on Dec. 14, 1976; 4,056,654 that issued to Kompanek on Nov. 1, 1977; and 4,636,908 that issued to Yoshihara et al on Jan. 13, 1987. For an optical switch employing a layer of PLZT see U.S. Pat. No. 4,715,680 that issued to Kawaguchi et al on Dec. 29, 1987.
Among the problems encountered have been microcracking in the thin films due to thermal mismatch and the incompatibility between substrates and the ferroelectric material due to crystal lattice mismatch. These problems of fabrication have adversely affected the widespread use of such ferroelectric thin film devices.